Recently, commercially available handheld apparatus, such as mobile phone and personal digital assistant (PDA) requires two display panels for providing some additional functions, such as digital camera. For a folding mobile phone having a digital camera, for example, the front secondary display panel is used for time, phone number or caller ID display, while the inner primary display panel is used for text, picture or video display. When a user is desirous of taking a photo shot on an object except for himself, the inner primary display panel is used for viewing window to monitor the lens of the digital camera for the purpose of alignment of the lens to the object, while the user is anxious for taking photo shot for himself, the lens of the digital camera can be monitored by the front secondary display panel as the viewing window.
There are many combinations for a dual panel display, so that it is hard to provide the total power solution for various power requirements. Specifically, due to different power supplies required for each of the panels, power supplies sufficient for individual panels must be provided. Two schemes are currently designed for individually turning each display panel on and off. In the first one, as illustrated in FIG. 1, an input voltage VIN from power source is converted to an output voltage VOUT by a controller chip 100 to supply to the backlight sources 104 and 108 of display panels 102 and 106 through an output voltage pin LX. The overvoltage protection signal OVP is generated by detecting the output voltage VOUT, a feedback signal FB is provided from the node between the backlight source 104 and a resistor R1, and an input signal CE is to provide a chip enable signal or dimming control signal to adjust the brightness of the backlight source 104. Since only the backlight source 104 is controlled by the controller chip 100, the other one, i.e., the backlight source 108, is permanently lighted up, resulting in high power consumption thereof. Alternatively, as illustrated in FIG. 2, two controller chips 200 and 202 are used for controlling the backlight sources 208 and 210 of panels 204 and 206, respectively. Even the power consumption is reduced by using two controller chips 200 and 202 individually controlling the backlight sources 208 and 210, the cost is higher for two chips 200 and 202 are used.
As shown in FIGS. 1 and 2, the conventional backlight system of a dual panel display handheld apparatus requires two controller chips to fully control the two display panels thereof, otherwise one of them has to be left out of control. Moreover, the conventional backlight controller chip provides only positive voltage, and it is therefore not capable of applying to organic light-emitting diode (OLED) display panel. For the purpose of obviating aforementioned disadvantages, it is desired a single backlight power controller chip for full control of a dual panel display in a handheld apparatus, and for application to various types of dual panel display.